My mind must be getting a little loose. I always thought heating was accomplished by offering the biggest difference in temperature between the room and the heating element. Faster flow rates and higher temps realise higher return temps. Why temper the boiler water with the return? Does't that mean that several pumps are going to run for extended periods of time? More tons of coal? Simple always worked better for me. Perhaps running a separate zone to the "dumper" and using the two candles to read by is a warmer means to an end. Scott

stokerscot wrote:My mind must be getting a little loose. I always thought heating was accomplished by offering the biggest difference in temperature between the room and the heating element. Faster flow rates and higher temps realise higher return temps. Why temper the boiler water with the return? Does't that mean that several pumps are going to run for extended periods of time? More tons of coal? Simple always worked better for me. Perhaps running a separate zone to the "dumper" and using the two candles to read by is a warmer means to an end. Scott

Thats old tech thinking - sorry please don't take that as a slap - its the same as we all used to think the only place for a circulator was on the return. Modern pumps are now able to live on the supply and if you read "Pumping Away" by Dan at http://www.heatinghelp.com/shopcart/product.cfm?category=8-191This link is broken, either the page no longer exists or there is some other issue like a typo. you will have a better understanding why.

Cooler lower gpm flow at a more constant rate in load loops produces a more efficient, constant, comfortable room - vs - hi temp circulation and bang bang on off circulation that overheats a radiator and causes hi low temperature swings in the room just like forced scorched air heating does.

Why temper the water back to the boiler??? So the boiler isn't introduced to large swings in temperature caused by circulating cold zone water directly back to it. But if you circulate cooler water longer that possibility is also greatly reduced. Yes that means the circ pumps will run longer - but now we use low wattage modern cartridge pumps that do not cost an arm and a leg to run - plus you run the boiler less and you use less solid fuel, you also have less thermal expansion cycles on engine and energy transmission piping.

You like my dumper analogy? Gotta keep warm somehow sometimes!

Down load the free heat loss calculator from http://slantfin.com/heat-loss-software.htmlThis link is broken, either the page no longer exists or there is some other issue like a typo. - measure the radiation of each loop and the heat loss of each area and you can calculate just how low a temperature of water you can circulate to maintain design room comfort vs outdoor temperature. The less energy you need to produce in the boiler to heat you place the less fuel you need to buy and the huge side benefit - you will be more comfortable with cooler radiators because the rooms will be evenly, gracefully, quietly, heated.

First thing that needs addressing is your willingness to try peddling your books at the expense of a great website. If all the books that you reference were purchased, it would be enough for another ton of coal. While your argument is sound, yes you are technically right, your way of hooking up hydronic systems would show greater fuel efficiency for far larger systems that what most of us here are using. The application of many costly, unnecessary parts,parts that will cost several times their initial install value to repair or service(speed drives), will make the overall efficiency higher but , really, how hard can you make it to hook 2 boilers together? In my opinion there has been two choices offered on this thread that are tough to beat by their simplistic nature, their economy of parts, their overall reliability, their ease of install, their avoidance of high tech failure prone parts, and the local availability of parts should one fail. Neither choice was put forth by you. It is also my opinion that the latest in new school thinking is the reason that prices are so elevated. Frankly, even though your engineering skill would survive all "challenges", you are not the guy I would want to involve when putting a system in my house. Coaledsweat would defineately be the guy. Scott

Thats a good point Scott! When you buying fuel for under 100.00 bucks a ton, a simply plant and load system will return an ROI faster than a complicated one. I don't have any affiliations - these are not 'my' books - mine have been "relocated" - I simply offer a resource to learn with. Sort of like - Give a man a fish and he eats for a day, but teach a man to fish and he can hide a drinking problem - or something like that

Well anyway hope some folks found some help in an "alternative view" and very glad you found a comfort level because of it!I will atone to be guilty to have explored several ways to accomplish the same goal - but if we go back to my first suggestion of only breaking into the return of the existing (legacy) system with two close spaced tees - all the "complicated' equipment is one aquastat to control one small watt draw pump. That to me was the easiest and quickest way to install my biomass boiler when my fuel was 40% of the cost of NG. Off season this year Ill tear that out for one of the more complicated primary secondary loop system to reduce expensive fuel use as coal is a bit more in Wisconsin these days.

Again sorry that you misunderstood my reading list and a peddlers rant. I have noted that the moderators are very strict about those things and would have edited or blocked me if that was my intent. Please understand it was not. Just offering my words here - thats all!

Sting, your view as well as mine, are the reason this is an open forum. I really didn't mean to accuse you of book thumping . It's just that too many really cool websites are taken over by anyone willing to punch a keyboard. Right now it is the two of us that are guilty. I apologise to other members for the disruption of probably one of the best threads going right now. It is a discussion that should take place with a beer in hand. Scott

I'm going to post again my method and suggestion, it follows the KISS principle; Keep I Simple Stu.... !!

Plumb the coal boiler into the return line before it enters the oil boiler... This way the cool return water from the house will be preheated before it gets to the oil boiler. Set the aquastat on the coal boiler 40* hotter than the aquastat on the oil boiler. The oil boiler won't come on unless the coal system is out.

You could install an electric damper in the oil boiler's flue... tied to the oil burner.. this eliminates heat loss up the oil boiler's chimney.

You can use the existing circulator pump, an additional one is not needed

So buy the coal boiler, some associated plumbing to connect it inline with the oil boiler, and buy and install an electric flue damper for the oil boiler..

This is the shortest items-to-purchase list. the simplest way, and IT WORKS..

I think this thread should be retitled to something like 'I need a bicycle, can someone tell me how to make a Space Shuttle?'

It should get real interesting now. I spoke with the plumber. He said there is no code issue with the PRV and you can plumb anything you want to it, the PRV goes at the top of it. He had no problem with a reverse flow through the gas/oil boiler.

I spoke to the PE, he would not recommend heating domestic water from a solid fuel appliance. His reason being, in a solid fuel appliance, an overheat condition could deliver extremely hot water. Use of a tempering valve in this case is a poor choice for safety reasons. He recommended pulling another zone to a Boilermate style storage tank. Forty to eighty gallons depending on your family's size. (I wonder why all these coal/wood/corn/pellet/banana peel boiler manufacturers offer tankless coils if its a bad idea?) He had a problem with reversing the flow through the gas boiler but I couldn't get a reason why, I don't think he knew why. To top it off, he offered up a drawing that has me scratching my head.

Greg, with what you described, what happens when the coal boiler fails to make heat? If you are describing a single loop, when carrying the load the gas/oil will be giving up heat to the coal boilers chimney. If you are on gas/oil all summer, that is going to cost you some serious coin.